Search found 50 matches
- Sat Mar 17, 2018 1:53 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Lyndon Review Test, Question 7a [ENDORSED]
- Replies: 7
- Views: 949
Re: Lyndon Review Test, Question 7a [ENDORSED]
Catalysts are usually shown in the reaction equation above the "======>" arrow. For example, if potassium iodide is the catalyst in a reaction then "KI" will be written above the "======>" reaction arrow.
- Sat Mar 17, 2018 1:31 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Meaning behind E
- Replies: 1
- Views: 326
Re: Meaning behind E
Cell potential is the potential voltage that a galvanic cell can exhibit based on the reduction potentials of its redox reactions. A substance with a higher reducing power is more likely to be oxidized, meaning that it is most "willing" to give up electrons in order to reduce other substan...
- Sat Mar 17, 2018 1:22 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: acidic/basic
- Replies: 2
- Views: 441
Re: acidic/basic
It depends on which side needs to be balanced in terms of excess hydrogen. If the solution is acidic, H+ would be added to whichever side that needs more hydrogen atoms to balance the redox equation, whereas OH- would be added in redox equations in basic solutions.
- Sat Mar 10, 2018 10:06 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Temperature and equilibrium constant [ENDORSED]
- Replies: 2
- Views: 404
Re: Temperature and equilibrium constant [ENDORSED]
Raising the temperature in a reaction typically increases the rate at which the reaction proceeds (k) since the increased average kinetic energy of the particles in the reaction causes more reactants to collide with other reactants to form products.
- Sat Mar 10, 2018 10:00 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Changes with Temperature [ENDORSED]
- Replies: 2
- Views: 341
Re: Changes with Temperature [ENDORSED]
Typically, k increases as the temperature increases because heat increases the average kinetic energy of the particles in a reaction, increasing the likelihood that two reactants will meet and thus react.
- Sat Mar 10, 2018 9:48 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: activation energy [ENDORSED]
- Replies: 3
- Views: 758
Re: activation energy [ENDORSED]
Activation energy is the main determinant in the kinetic stability of a reaction. For instance, a reaction is kinetically stable if the activation energy is exceedingly high (i.e.; the conversion of carbon (diamond) into carbon (graphite) since said reaction would take a high amount of energy to und...
- Sun Mar 04, 2018 10:13 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Little Product
- Replies: 4
- Views: 668
Re: Little Product
For reactions with multiple reactants, we also tend to use a small amount of one reactant and excess of the other reactants in order to study the order of each reactant. For example, in a reaction A + B + C ====> D, we would use A and C in excess and a small amount of B to determine its order with r...
- Sun Mar 04, 2018 8:38 pm
- Forum: General Rate Laws
- Topic: catalytic reaction
- Replies: 5
- Views: 677
Re: catalytic reaction
Countless biological chemical reactions are also catalyzed by proteins, such as the metabolization of lactose using lactase.
- Sat Mar 03, 2018 11:20 pm
- Forum: First Order Reactions
- Topic: half life
- Replies: 2
- Views: 402
Re: half life
Half-life deals with finding the time it takes one reactant to decompose to half of its original mass, so there cannot be "multiple reactant" half-life problems.
- Mon Feb 26, 2018 12:24 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: What other elements could be used besides Pt?
- Replies: 5
- Views: 725
Re: What other elements could be used besides Pt?
Christy Zhao 1H wrote:How do you know when to use Pt or graphite?
It usually specifies whether platinum or graphite is used, but both serve the same purpose. However, a Pt(s) electrode is more commonly used.
- Mon Feb 26, 2018 12:09 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: standard conditions [ENDORSED]
- Replies: 4
- Views: 613
Re: standard conditions [ENDORSED]
Most chemical experiments occur at STP, or Standard Temperature and Pressure, where the reaction occurs at 25 C (298 K) and 1 atm of atmospheric pressure. The reason for using STP is to allow other scientists to easily reproduce the conditions for the experiment.
- Mon Feb 26, 2018 12:03 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge [ENDORSED]
- Replies: 2
- Views: 402
Re: Salt Bridge [ENDORSED]
I believe that there is no advantage to using a salt bridge over a porous membrane. Both work by allowing the charged ions to move from one solution to another in order to keep the charge flowing. If there was no salt bridge, the charged ions (say, Fe3+) would accumulate in one beaker and no electri...
- Mon Feb 19, 2018 6:14 pm
- Forum: Balancing Redox Reactions
- Topic: H+ or H3O+
- Replies: 2
- Views: 366
Re: H+ or H3O+
It shouldn't matter; they're both the same thing. I just use H+ for the sake of saving time and ink.
- Mon Feb 19, 2018 6:11 pm
- Forum: Balancing Redox Reactions
- Topic: 14.5 part d
- Replies: 7
- Views: 857
Re: 14.5 part d
You would only add H2O to balance out the number of oxygen atoms in a reaction. Otherwise, to balance the number of hydrogen atoms in a redox reaction, you would add H+ ions to whichever side as needed. Then to balance the charges, you would add electrons as necessary. In this case, the reaction wou...
- Sun Feb 11, 2018 2:39 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Entropy and compression
- Replies: 3
- Views: 1680
Re: Entropy and compression
A greater volume (lower pressure) allows for more room for the molecules to occupy, increasing the potential for degeneracy in the system. Think of it in terms of one mile of crowded freeway; the more lanes there are for cars to move about, the more combinations of different cars there can be in tha...
- Sun Feb 11, 2018 2:35 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Derivations of Equations
- Replies: 5
- Views: 662
Re: Derivations of Equations
I doubt that we would have to know any other equation other than those provided on the equation sheets. The derivations are taught most likely to provide a basis of understanding on where the equation came from and how they relate to one another, rather than just name dropping a formula.
- Sun Feb 11, 2018 2:34 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Quantity of reversible vs. irreversible work
- Replies: 2
- Views: 389
Re: Quantity of reversible vs. irreversible work
This is because in an isothermal reversible expansion process all energy is converted into useful work, whereas in isothermal irreversible expansion some energy is lost in the form of entropy; therefore, the work value of the latter would be less than the former.
- Sun Feb 11, 2018 2:32 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Irreversible Expansion
- Replies: 3
- Views: 551
Re: Irreversible Expansion
The delta S (surroundings) for irreversible expansion is zero because some of the energy was lost in the form of entropy (whereas in reversible expansion, all energy is converted into useful work), so the overall change in entropy (delta S (total)) has to be a positive number. The system is also iso...
- Sun Feb 04, 2018 2:15 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: second law of thermodynamics
- Replies: 2
- Views: 309
Re: second law of thermodynamics
Think of 0 K as a theoretical limit, where entropy is a function of the temperature in Kelvin. As T approaches 0 K, so would entropy; but since we cannot achieve 0 K, we can only approach zero entropy.
- Sun Feb 04, 2018 2:07 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Assume ideal gas?
- Replies: 4
- Views: 576
Re: Assume ideal gas?
I believe that we assume ideal gas behavior for the sake of understanding the basis of the concept. Calculating for non-ideal gas behavior before understanding the ideal gas behavior would most likely be more confusing because the former requires more to be taken into account.
- Sun Feb 04, 2018 1:43 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Pulley and Vacuum
- Replies: 2
- Views: 421
Re: Pulley and Vacuum
Without the weight pulley controlling the gas's volume, the gas would expand throughout the container because of the positive pressure it exerts against the vacuum. Adding weight to the pulley will counteract the pressure exerted by the gas, compressing said gas in the container -- whereas removing ...
- Sat Jan 27, 2018 6:19 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Out of Topic
- Replies: 3
- Views: 558
Re: Out of Topic
I've heard that Dr. Lavelle's office hours may be busy at times, so seeing a TA or making use of the Peer Learning Sessions may be viable options as well. All of these hours can be found on the 14B website!!
- Sat Jan 27, 2018 6:09 pm
- Forum: Phase Changes & Related Calculations
- Topic: Calculating the Change in Enthalpy
- Replies: 4
- Views: 677
Re: Calculating the Change in Enthalpy
As Clarisse said, the heat of fusion/vaporization should be given. You would then need to determine which value to use (heat of vaporization for phase changes between liquids and gases, and heat of fusion for phase changes between liquids and solids), where you would then multiply the value by the m...
- Sat Jan 27, 2018 6:06 pm
- Forum: Phase Changes & Related Calculations
- Topic: enthalpy of fusion/vaporization
- Replies: 3
- Views: 435
Re: enthalpy of fusion/vaporization
It helps to consider whether the phase change is exothermic or endothermic, because then you'll know if heat is being absorbed or released. The heat of vaporization from a liquid to a gas is positive because it is an endothermic phase change that requires energy, whereas the heat of fusion from a li...
- Sun Jan 21, 2018 5:00 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Constant Volume vs Constant Pressure
- Replies: 6
- Views: 554
Re: Constant Volume vs Constant Pressure
Because W (work) = PdV (pressure times a change in volume), work cannot be done if there is no change in volume since the dV value would equal 0.
- Sun Jan 21, 2018 4:42 pm
- Forum: Phase Changes & Related Calculations
- Topic: Equations to know
- Replies: 6
- Views: 457
Re: Equations to know
I doubt that we will have to memorize any enthalpy values or heats of vaporization/fusion, but it may be helpful to have the 4.18 j/gc value handy when doing heat calculations involving water.
- Sun Jan 21, 2018 4:40 pm
- Forum: Phase Changes & Related Calculations
- Topic: 8.9
- Replies: 2
- Views: 383
Re: 8.9
To convert L/atm to Joules, you would multiply the L/atm amount by 101.325 joules, since 1 L/atm = 101.325 joules.
- Thu Jan 11, 2018 9:31 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Celsius the same as Kelvin? [ENDORSED]
- Replies: 9
- Views: 6572
Re: Celsius the same as Kelvin? [ENDORSED]
A change in degrees Celsius would be equivalent to the change in degrees Kelvin.
- Thu Jan 11, 2018 9:08 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Can homework be written in pencil?
- Replies: 6
- Views: 619
Re: Can homework be written in pencil?
It probably varies from TA to TA, but I don't see why pencil would be a problem! Tests should be in pen, though.
- Thu Jan 11, 2018 9:05 pm
- Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
- Topic: aqueous equilibria
- Replies: 2
- Views: 1304
Re: aqueous equilibria
I believe that it is covered in 14BL, however.
- Sat Dec 09, 2017 5:35 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Remembering VSEPR
- Replies: 3
- Views: 647
Re: Remembering VSEPR
The way I remember them is that I remember the shapes that have the largest number of bonding atoms, like octahedral and tetrahedral. If lone pairs replace the bonding atoms in a molecule, I picture the shape without a bonding atom at a point (ex; tetrahedral + 1 lone pair in place of an atom = trig...
- Sun Dec 03, 2017 10:06 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: When can a tetrahedral be non polar? [ENDORSED]
- Replies: 4
- Views: 4175
Re: When can a tetrahedral be non polar? [ENDORSED]
A symmetrical molecule cannot be polar, regardless if the bonds within the molecule are polar or not.
- Sun Dec 03, 2017 9:40 pm
- Forum: Dipole Moments
- Topic: Dipole Moments
- Replies: 2
- Views: 588
Re: Dipole Moments
Dipole moments usually pertain to an unequal distribution of electrons in a molecule. This unequal distribution arises as a result of highly-polar bonds and asymmetry within the molecule, where the charged electrons of a molecule reside together on one end of the molecule. For instance, water has a ...
- Sun Dec 03, 2017 9:34 pm
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: Molecular Orbital Theory
- Replies: 4
- Views: 444
Re: Molecular Orbital Theory
It shouldn't be on the final because it was not covered in any class or discussion section as far as I'm concerned
- Sun Dec 03, 2017 9:32 pm
- Forum: Sigma & Pi Bonds
- Topic: What is a localized and delocalized Bond?
- Replies: 5
- Views: 32681
Re: What is a localized and delocalized Bond?
A delocalized bond usually involves resonance between different bond types. For example, the double and single bonds of each carbon in a benzene ring resonate between double in single bonds; therefore, the double bonds are delocalized because they are not defined to a certain region.
- Mon Nov 27, 2017 10:42 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: #4.29? Determining which isomer has the largest dipole moment?
- Replies: 2
- Views: 654
Re: #4.29? Determining which isomer has the largest dipole moment?
Think of it in terms of polarity; if a charge is concentrated on one side of the molecule and not the other, then the molecule will be polar, but if the charges are evenly distributed then the molecule's polarity will cancel out.
- Mon Nov 27, 2017 10:27 pm
- Forum: Lewis Structures
- Topic: N2H6
- Replies: 2
- Views: 5266
Re: N2H6
That structure with a double bond would work IF nitrogen broke the octet rule, but it cannot since its principle quantum number is 2 and there is no 2d orbital.
- Sat Nov 18, 2017 6:42 pm
- Forum: Biological Examples
- Topic: Other Biological Examples
- Replies: 5
- Views: 999
Other Biological Examples
I really found the whole TM and biological significance section interesting. What are some other examples of vital TM complexes other than the ones we learned in class?
- Sat Nov 18, 2017 6:31 pm
- Forum: Balancing Chemical Reactions
- Topic: Combustion Question
- Replies: 9
- Views: 1401
Re: Combustion Question
For the sake of simplicity and this class, complete combustion always results in the production of gaseous H2O and CO2. In reality, combustion produces many other compounds, such as CO.
- Thu Nov 16, 2017 10:45 pm
- Forum: Ionic & Covalent Bonds
- Topic: SiO2
- Replies: 4
- Views: 6126
Re: SiO2
SiO2 is polar based on the electronegativity differences between Silicon and Oxygen, which can be interpreted from the periodic table. Although the SiO2 molecule itself is non-polar due to symmetry, the bonds between the Si and O atoms are polar.
- Thu Nov 02, 2017 11:17 pm
- Forum: Ionic & Covalent Bonds
- Topic: Chemical bonds create lower energy?
- Replies: 4
- Views: 510
Re: Chemical bonds create lower energy?
To add to the previous statement (which also added to its previous statement), atoms bond to achieve noble gas configuration, which is considered low-energy and stable.
- Thu Nov 02, 2017 11:14 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Reasonable Model
- Replies: 2
- Views: 299
Re: Reasonable Model
Unless the object of interest is a photon, then said object's velocity should be slower than the speed of light. Any velocity that exceeds the speed of light would be unreasonable.
- Mon Oct 30, 2017 11:17 pm
- Forum: Ionic & Covalent Bonds
- Topic: determining bonds
- Replies: 4
- Views: 568
Re: determining bonds
Generally speaking, bonds between metals and nonmetals form ions when they bond, so a metal/nonmetal bond is an ionic bond. A covalent bond occurs between nonmetals, and a metallic bond is a bond between metal elements.
- Mon Oct 30, 2017 11:10 pm
- Forum: Lewis Structures
- Topic: Knowing compound formulas
- Replies: 3
- Views: 531
Re: Knowing compound formulas
In my high school we were required to memorize a list of polyatomic ions, which included the formulas for compounds such as ammonium and sulfate. I haven't heard much about having to do the same here at UCLA yet, but it would only be beneficial to know the formulas.
- Sat Oct 21, 2017 9:59 pm
- Forum: SI Units, Unit Conversions
- Topic: Quantum Mechanics
- Replies: 4
- Views: 801
Re: Quantum Mechanics
Generally speaking, electron affinity increases up a group and across a period. This is mainly due to the shielding of electrons and an electron's "desire" to achieve noble gas configuration. For instance, fluorine has a higher electron affinity than oxygen because the former only needs on...
- Sat Oct 21, 2017 9:43 pm
- Forum: Properties of Light
- Topic: the quantum world
- Replies: 7
- Views: 826
Re: the quantum world
It'd probably be beneficial to know that a photon with a wavelength of 400-700 nm lies in the visible light spectrum, that a photon with a wavelength shorter than 400 nm is typically ultraviolet or higher energy particles (x-rays, gamma rays), and that 800 and above corresponds to infrared or lower-...
- Tue Oct 10, 2017 5:31 pm
- Forum: Properties of Light
- Topic: Chapter 1: Exercise 15
- Replies: 4
- Views: 916
Re: Chapter 1: Exercise 15
Wavelength is given instead of frequency most likely because the creators of the book wished for you to do an extra step to make the problems more complex. However, you can find the frequency from wavelength using c=lambda*nu, where lambda is the wavelength and nu is the frequency. Just rearrange th...
- Tue Oct 10, 2017 5:20 pm
- Forum: Trends in The Periodic Table
- Topic: Which is larger O - or S 2- ? [ENDORSED]
- Replies: 3
- Views: 2672
Re: Which is larger O - or S 2- ? [ENDORSED]
S2- is larger than O- because S2- has more protons and thus a stronger pull on its electrons than O- does, so it has a smaller atomic radius.
- Tue Oct 03, 2017 9:31 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3869922
Re: Post All Chemistry Jokes Here
I was gonna make a funny chemistry joke.
But they argon.
But they argon.
- Tue Oct 03, 2017 9:16 pm
- Forum: Ionic & Covalent Bonds
- Topic: Ionic Bonds
- Replies: 3
- Views: 560
Re: Ionic Bonds
Generally speaking, cations (positive ions) are typically metals which lose their electrons in an ionic bond, while anions (negatively charged ions) are typically nonmetals which gain electrons in an ionic bond. For example, in KCl, the metal K loses it's electron based on the aforementioned rule, w...